Inkjet printing mechanisms use pens which shoot drops of liquid colorant, referred to generally herein as "ink," onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, both assigned to the present assignee, Hewlett-Packard Company. In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a "service station" mechanism is mounted within the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include an elastomeric capping system which hermetically seals the printhead nozzles from contaminants and drying. To facilitate priming, some printers have elastomeric priming caps that are connected to a pumping unit to draw a vacuum on the printhead. During operation, partial occlusions or clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a clearing or purging process known as "spitting." The waste ink is collected at a spitting reservoir portion of the service station, known as a "spittoon." After spitting, uncapping, or occasionally during printing, most service stations have a flexible elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself. To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solids content than the earlier dye-based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper. Unfortunately, the combination of small nozzles and quick-drying ink leaves the printheads susceptible to clogging, not only from dried ink and minute dust particles or paper fibers, but also from the solids within the new inks themselves. Partially or completely blocked nozzles can lead to either missing or misdirected drops on the print media, either of which degrades the print quality. Thus, spitting to clear the nozzles becomes even more important when using pigment-based inks, because the higher solids content contributes to the clogging problem more than earlier dye-based inks.
Challenges were also faced in finding suitable capping strategies for the new pigment based inks, while also adequately capping the multi-color dye based printhead. Capping hermetically seals the area around the printhead nozzles to prevent drying or decomposition of the ink during periods of printer inactivity. The Hewlett-Packard Company's DeskJet.RTM. 850C color inkjet printer employed a elastomeric, multi-ridged capping system to seal the pigment based black pen. A spring-biased sled supported both the black and color caps, and gently engaged the printheads to avoid depriming them. A vent system was required including an elastomeric vent plug and a labyrinth vent path under the sled to avoid inadvertent over pressurizations or under pressurizations, like barometric changes in the ambient pressure or from volume changes during the capping process.
Thus, it would be desirable to find new ways of sealing an inkjet printhead, beyond mere modifications of the conventional elastomeric caps, and new ways of dealing with ink spit from printheads, beyond the conventional spittoons, along with new ways of sealing an inkjet printhead prior to installation in an inkjet printing mechanism.